阅读下面的短文，并根据短文内容回答所提问题。    Most teens need more than 9 hours of sleep each night. But about 1 in 4 teens has trouble in sleeping. Lack（缺少）of sleep can affect everything from our feelings to how well we focus on tasks like studying. It can also influence sports performance, increase our chances of getting sick, and may be related to weight gain in some people.
    How can we get the sleep we need? Here are some ideas:
    Be active during the day. Get at least 60 minutes of exercise a day. Physical activity can decrease（减少） stress and help people feel more relaxed. Just don't work too close to bedtime because exercise can wake you up before it slows you down.
    Say goodnight to electronics. Experts suggest using the bedroom for sleep only. At least shut everything down an hour or more before lights out.
    Keep a sleep routine（常规）. Going to bed at the same time every night helps the body expect sleep. Creating a set bedtime routine can improve this relaxation effect. Spending time with a pet, writing a diary or doing anything else can relax you.
    Expect a good night's sleep. Instead of worrying that you won't sleep, remind（提醒）yourself that you can. Say "Tonight, I will sleep well" several times during the day. It can also help to practice breathing exercises or gentle exercises before bed.
    Everyone has a sleepless night once in a while. But if you regularly have trouble in sleeping and you think it's affecting your mood or performance, talk to your doctor.